1. Field of the Invention
The present invention relates to a stator element for a Holweck pump stage, to a vacuum pump having a Holweck pump stage and to a method of manufacturing a stator element for a Holweck pump stage.
2. Description of the Prior Art
Vacuum pumps are used in various areas of technology such as, for example, in semiconductor process technology to generate a vacuum required for the respective technical process in a volume to be evacuated. An important pump mechanism used in vacuum pumps is the Holweck pump mechanism which is particularly effective in the molecular flow area and is called a molecular pump mechanism. Holweck pump stages are used e.g. in turbomolecular pumps which comprise, in addition to one or more turbomolecular pumps stages, one or more Holweck pump stages connected downstream of the turbomolecular pump stages. The Holweck pump stages can pump to one another in series or in parallel.
A Holweck pump stage typically comprises a stator element of substantially cylinder jacket shape and a rotor element, likewise of substantially cylinder jacket shape, with a jacket surface of the stator element and a jacket surface of the rotor element forming the surfaces of the pump stage provided with pump activity and being disposed opposite one another while forming a narrow gap which is called a Holweck gap. As a rule, a plurality of helical webs extending in the axial direction and grooves arranged between the webs and likewise extending helically in the axial direction are formed in the jacket surface of the stator element. The oppositely disposed jacket surface of the rotor element can e.g. be smooth.
The pump effect of the Holweck pump stage is based on the fact that the gas molecules to be conveyed are driven forward within the grooves by the rotating movement of the rotor element and are thereby conveyed in the axial direction, with the webs formed between the grooves sealing the grooves and preventing or reducing an outflowing or a backflowing of the gas molecules against the pumping direction.
Since a gap dimension of the Holweck gap which is as small as possible is inter alia necessary for a high pump efficiency, the stator element must be manufactured with high precision and within tight production tolerances.
Since the stator element of the Holweck pump stage is additionally directly in communication with the conveyed gases and is exposed to high thermal and mechanical loads, the material of the stator element must be selected such that a contamination of the vacuum is precluded, a sufficient vacuum tightness is ensured and the stator element withstands the thermal and mechanical loads. To satisfy this demand, stator elements for Holweck pump stages are typically milled out of solid cylinders or out of hollow cylinders composed of a vacuum-compatible metal, which is associated with a very high time and cost effort.
An object of the invention is to provide a stator element for a Holweck pump stage which satisfies the technical vacuum demands and which can be manufactured with a reduced time effort and cost effort and to provide a method of manufacturing a stator element for a Holweck pump which can be carried out with a reduced time effort and cost effort.